Message.args and Message.kwargs were a bare tuple and dict, Broker.queues
held a bare Queue, emit_before/emit_after took an untyped signal, the
actor-facing Broker methods used a bare Actor, and Cancel.backend had no
type at all. Strict type checkers in downstream code reported every use of
them as partially unknown.

They are now tuple[Any, ...], dict[str, Any], Queue[bytes] | None, str,
Actor[..., Any] and CancelBackend | None. No runtime change.